Mortgage Bond Investors Seek 'Obama Button' to Divine Trades

NEW YORK—Investing in the $5 trillion agency mortgage-backed securities market has long been a technician's game, with statistics and mathematical formulas frequently guiding investor decisions.

But the last few years have seen greater uncertainty in predicting key variables—in particular how fast homeowners will repay their loans—because federal policy makers have repeatedly changed the rules of the mortgage game via the Obama...